To measure pressure in fluid systems, differential pressure sensors are often used in combination with some sort of valve assembly, which has a primary purpose of protecting the differential pressure sensor against extreme continuous pressures or pressure shocks that are higher than the sensor can handle. Such assemblies often also have functions for flushing the assembly to get rid of enclosed air in cavities and have functions to calibrate the differential pressure sensor, a so called zero point calibration. The purpose of the calibration procedure is to ensure that before measuring begins, both measuring sides of the pressure sensor have the same pressure.
There are several examples of devices that have a manual flushing function, for instance U.S. Pat. No. 5,868,155 A1 and WO 2005019713.
There are also devices that solve the problem with the zero point calibration and flushing of the valve assembly by a manual procedure. One example of such a solution is shown in GB 2 410 332 A, in which a manual controllable valve (30, 40) fluidly connects both pressure sides, and accordingly, the system is flushed and zero point calibrated.
The problem with earlier solutions, for instance the solution described by GB 2 410 332 A, is that by the zero point calibration of the differential pressure sensor, the high and low pressure side is connected by fluid, which results in that the zero point will be dependent on the rate of flow of the fluid through the valve assemble and the thereby caused pressure drop, which leads to that an error will be caused by the calibration. There is a solution of this problem according to the device in JP 63011827 A where the high and low pressure side, by calibration, isn't in contact with the fluid, but this device don't solve the problem of at the same time and automatically be rid of enclosed air in the valve.